Prior art techniques for detecting fluorescence from a capillary used in DNA sequencing are well known.
Narrowband approaches typically call for filtering the fluoresced light into discrete bands, through the use of discrete filter elements or filter wheels, followed by further processing and comparison of the resulting output. Such approaches are rather limited in the quality and volume of data that can be used for nucleotide identification.
Multi-wavelength approaches, such as that described in Karger, A. et al., Multiwavelength Fluorescense Detection For DNA Sequencing Using Capillary Electrophoresis, Nucleic Acids Research, v. 19, no. 18, pp. 4955-4962, use a spectrometer to separate the light into multiple bands for subsequent analysis. However, spectrometers and the associated equipment used, as shown in FIG. 1 of this reference, are both expensive and bulky. The spectrometer used in this figure typically comprises an entrance slit to spatially limit the incoming light; a collimator lens having a focal point coincident with the position of the entrance slit so as to convert the light emerging from the slit into parallel rays; a reflection diffraction grating to diffract the parallel rays from the collimator lens to produce spectra; and an imaging lens to focus the diffracted parallel rays onto a CCD imaging plane. Thus, the arrangement of FIG. 1 in this reference is expensive, bulky and has low light throughput.